Manufacturers of printers often create fonts to be used by the printer. These fonts are often referred to as printer fonts. These printer fonts are usually embedded in devices associated with the printer. Examples of devices with embedded fonts include font cartridges and memory modules.
Since the fonts reside on a device and not in the operating system, they are not readily accessible by software applications. A device driver for the printer communicates with the software application to allow software applications to use the printer fonts when printing to the printer.
Differences in output will occur when a document is created using one of the printer fonts, then printed on a different printer using a printer driver that knows nothing about the printer font used in the document. The device driver for the printer used to print the document will not properly handle the printer font that it knows nothing about. Instead, the device driver will print an approximation of the font.
Printer metrics files describe the characteristics of specific fonts that are embedded in the devices. Printer metrics files are often referred to as printer font metrics (PFM) files and printer cartridge metrics (PCM) files. PCM files are typically a collection of PFM files represented as one physical file. The printer driver reads the printer metrics files and uses the information contained in the printer metrics files to display an approximation of the printer font on a screen for a user to view.